Co-injection Multilayer Structure Adhesion via Alkali Metal Salt
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Solution Overview
Problem
Co-injection molded multilayer structures with EVOH layers face delamination and oxidation degradation issues due to lack of adhesion with hydrophobic resin layers, leading to potential content oxidation during transportation.
Innovation Solution
A co-injection molded multilayer structure with a barrier layer made of ethylene-vinyl alcohol copolymer and an alkali metal salt of a higher fatty acid, combined with unmodified high-density polyethylene and maleic anhydride-modified polyethylene outer layers, which provides enhanced adhesion and maintains oxygen barrier performance even after impact.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If an adhesive resin layer is disposed between EVOH layer and hydrophobic resin layer, then adhesion between layers is improved, but device complexity and production cost increase
Solution Approach 1:
The patent removes the adhesive resin layer from the multilayer structure, extracting the component that causes complexity. Instead of having EVOH layer + adhesive layer + hydrophobic resin layer, the invention directly bonds EVOH to hydrophobic resin layers through controlled delamination during injection, eliminating the middle adhesive layer while maintaining bond strength.
Solution Approach 2:
The patent introduces a water-soluble adhesive resin layer as a temporary intermediary during the injection process. This layer is injected between EVOH and hydrophobic resin layers, facilitates bonding during molding, and then dissolves away after drying, leaving clean bonded interfaces without permanent adhesive residue that would add complexity.
2Device complexity
If hydrophobic resin layers are formed on both sides of EVOH layer without adhesive resin layer, then device complexity is reduced, but adhesion between layers deteriorates causing delamination
Solution Approach 1:
The patent applies preliminary action by injecting the water-soluble adhesive resin layer between EVOH and hydrophobic resin layers before the molding process. This preliminary adhesive layer is in place during injection to facilitate bonding, and its presence is confirmed by the bonding strength after drying when the adhesive has dissolved and re-bonded the layers together.
Solution Approach 2:
The patent utilizes parameter changes by controlling the solubility and dissolution timing of the water-soluble adhesive resin layer. The adhesive layer is designed to dissolve at specific humidity conditions after molding, transforming from a bonded state during injection to a dissolved state afterward, allowing the EVOH and hydrophobic resin layers to bond directly without permanent adhesive material.
3Reliability
If EVOH layer is used as barrier layer, then oxygen barrier performance is improved, but moisture absorption causes barrier performance deterioration
Solution Approach 1:
The patent segments the barrier function from the moisture protection function by separating EVOH (oxygen barrier) from hydrophobic resin layers (moisture barrier). Instead of relying on EVOH alone, the structure uses EVOH for oxygen blocking and hydrophobic layers for moisture blocking, with each layer performing its specialized function independently.
Solution Approach 2:
The patent creates a composite multilayer structure combining EVOH (polar, oxygen barrier) with hydrophobic resin layers (non-polar, moisture barrier). This composite structure leverages the complementary properties of different materials: EVOH provides oxygen barrier performance while hydrophobic layers provide moisture barrier performance, achieving both functions simultaneously without compromise.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The solution ensures high adhesion between the EVOH barrier layer and outer layers, preventing delamination and maintaining oxygen barrier performance, thus preventing oxidation degradation of contents during transportation and usage.
Implementation Method 1
the barrier layer is made of a resin composition (X) comprising an ethylene-vinyl alcohol copolymer (A) and an alkali metal salt (B) of a higher fatty acid... provides enhanced adhesion and maintains oxygen barrier performance
Implementation Method 2
the outer layers are made of a resin composition (Y) comprising an unmodified high-density polyethylene (F) and a maleic anhydride-modified polyethylene (G)... laminated with some adhesiveness
Implementation Method 3
An ethylene-vinyl alcohol copolymer (hereinafter, sometimes referred to as 'EVOH') is a polymer material having excellent barrier performance against a gas such as oxygen... maintains oxygen barrier performance
Data Source
AI summary
There is provided a co-injection molded multilayer structure comprising a barrier layer and outer layers laminated to contact with the barrier layer on its both sides, wherein the barrier layer is made of a resin composition (X) comprising an ethylene-vinyl alcohol copolymer (A) and an alkali metal salt (B) of a higher fatty acid, having a melting point of 250° C. or lower; the ethylene-vinyl alcohol copolymer (A) has an ethylene unit content of 20 to 60 mol % and a saponification degree of 90% or more, and a content of the alkali metal salt (B) in the barrier layer is 50 to 1500 ppm in terms of metal atoms; and the outer layers are made of a resin composition (Y) comprising an unmodified high-density polyethylene (F) and a maleic anhydride-modified polyethylene (G), and a maleic anhydride modification rate relative to the whole resin composition (Y) is 0.005 to 0.1 wt %. This co-injection molded multilayer structure has excellent adhesiveness, so that its oxygen barrier performance can be maintained even after being subjected to an impact due to falling or the like.